According to the documentation for eglQueryString:
> EGL_BAD_DISPLAY is generated if display is not an EGL display connection,
> unless display is EGL_NO_DISPLAY and name is EGL_EXTENSIONS.
Therefore, we should check EGL by doing:
eglQueryString(EGL_NO_DISPLAY, EGL_EXTENSIONS)
Indeed, the old way of eglQueryString(EGL_NO_DISPLAY, EGL_VERSION) works on
libglvnd but not using mesa's libEGL.so directly.
Also added a warning to make it more obvious that EGL is not available.